Finding a good and accurate graphic or illustration for your need is something that we all struggle with. On top of that if the requirement is that the graphic resource has to be free (as in freedom) then it further narrows down the options. Sometimes you see the graphic you want, but its license terms are unknown or are not agreeable to your work as they are not released freely. So what do you do? Either you use an illustration which is not perfect fit or you use one which breaks your resource (in terms of license). But the problems is also that there are many free resource repositories which are very well not known. I have personally come across great many graphic resources, only to be forgotten after their current need is finished. This post is an attempt to overcome this. This post is a collection of various free graphics and illustration resources and repositories that I have found useful over the years. It is also a sort of personal bookmark list of the these resources if and when I need them in the future. I hope this will be of use to others too. I will keep on updating this list with new resources that I find. If you know of any resources which are missing please do post in the comments.
The Internet Archive Image Search https://archive.org/details/image
Wikimedia Commons https://commons.wikimedia.org/
Open source illustrations kit https://illlustrations.co/
NYPL Public Domain Archive https://nypl.getarchive.net
David Rumsey Map Collection https://www.davidrumsey.com/ also https://archive.org/details/david-rumsey-map-collection
Metropolitan Museum of Arts Public Domain Images also https://archive.org/details/metropolitanmuseumofart-gallery
Cleveland Museum of Art Open Access also https://archive.org/details/clevelandart
Brooklyn Museum also https://archive.org/details/brooklynmuseum
https://archive.org/details/bibliothequesaintegenevieve_image
Vintage Ads
Vintage British Print Ads https://archive.org/details/vintage-british-magazine-ads
Vintage American Print Ads https://archive.org/details/vintage-american-print-ads
Vintage Danish Print Ads https://archive.org/details/vintage-danish-print-ads
https://archive.org/details/vintage-new-zealand-print-ads
https://archive.org/details/vintage-canadian-print-ads
https://archive.org/details/vintage-italian-print-ads
A library of microorganisms https://archive.org/details/cmpuj
National Gallery of Art also https://archive.org/details/national-gallery-of-art-images
Flickr Collections (there are several collections on Flickr which are openly licensed)
NOAA Photo Library https://flickr.com/photos/noaaphotolib/
What about sites like pixabay and all?
yes will keep updating. these are some of my go to sites which are listed here